Electromagnetic pump stator frame

Abstract: A stator frame 24 for an electromagnetic pump 10 includes a casing 26 joined to a hub 28 by a plurality of circumferentially spaced apart struts 40. At least one electrically insulated power crossover lead 42 extends through the hub 28, through a crossover one of the struts 40, and through the casing 26 for carrying electrical current therethrough.

Description: The present invention relates generally to electromagnetic pumps, and, more specifically, to a stator frame therein for routing electrical power leads therethrough. BACKGROUND OF THE INVENTION Advanced nuclear reactors being developed include liquid metal nuclear reactors which use liquid sodium, for example, for cooling the reactor core thereof. In order to circulate the liquid sodium through the reactor core, electromagnetic pumps are used which magnetically pump the liquid sodium therethrough. More specifically, annular linear induction, or electromagnetic, pumps (ALIP) are known which include annular electrical coils and lamination rings which are stacked together on a common longitudinal centerline axis and have an annular duct extending therethrough. Electrical current provided to the coils induces magnetic flux for pumping the liquid metal through the duct. The coils may be arranged in a singular tubular configuration conventionally known as a single stator electromagnetic pump, or two groups of coils may be used, with the first group being configured in one tubular configuration as a radially inner stator, and the second group configured in another tubular configuration as a radially outer stator spaced radially outwardly from the inner stator to define a concentric annular flow duct therebetween in which the liquid sodium is propelled linearly through the electromagnetic pump parallel to its longitudinal centerline axis. The liquid sodium is pumped axially through the pump from its bottom inlet to its top outlet, or discharge plenum, wherein it turns radially outwardly away from the centerline axis of the pump. The stator coils of the pump are provided with electrical current through power leads which, in a single stator ALIP, are typically channeled downwardly through the discharge plenum and into the stator. In order to protect the power leads from the liquid sodium in the discharge plenum, suitable conduits, including bellows, surround the power leads and are therefore subject to flow induced vibration and provide a potential sodium leakage path in the event of damage thereto. Similarly, the power leads to the outer stator of a double stator ALIP may also be disposed in protective conduits including bellows where the power leads pass through the discharge plenum. In the double stator ALIP design, however, the power leads to the inner stator may be routed directly from a junction box extending upwardly from the inner stator along the pump centerline axis and disposed radially inside the discharge plenum. Accordingly, the inner stator power leads are inherently protected by the junction box and not exposed to the liquid sodium, whereas the outer stator power leads must still be protected by the separate conduits and bellows, the elimination of which is desired. JP-A-62 217 853 shows an arrangement with a crossover passage which extends from the hub, through the strut and to the casing. Summary of the Invention According to the invention, there is provided a stator frame for an electromagnetic pump comprising: an annular, radially outer casing; an annular radially inner hub disposed coaxially with said casing and spaced radially inwardly therefrom to define an annular inlet channel therebetween; a plurality of circumferentially spaced apart struts extending radially between said casing and said hub and through said inlet channel; and at least one power crossover lead extending through said hub, through a crossover one of said struts, and through said casing for carrying electrical current therethrough, a crossover passage extending through said hub, said crossover strut, and said casing for receiving said crossover lead therein; and said crossover passage having a tubular electrical insulator therein for receiving said crossover lead for electrically insulating said crossover lead from said hub, said crossover strut, and said casing, characterised in that said crossover passage includes a center channel extending radially from said hub and through said crossover strut into said casing; a hub channel extending perpendicularly from an inner end of said center channel to an inside surface of said hub; and a casing channel extending perpendicularly from an outer end of said center channel to an inside surface of said casing; said crossover lead includes a center conductor extending through said center channel; a hub conductor extending through said hub channel and electrically joined to said center conductor; and a casing conductor extending through said casing channel and electrically joined to said center conductor; and said electrical insulator includes a center bushing surrounding said center conductor in said center channel and extending radially between said hub conductor and said casing conductor; a hub bushing surrounding said hub conductor in said hub channel; and a casing bushing surrounding said casing conductor in said casing channel. Brief Description of the Drawings The invention will now be described in greater detail, by way of example, with reference to the drawings in which: Figure 1 is a longitudinal sectional view of an exemplary double stator electromagnetic pump having an improved stator frame including power crossover leads in accordance with one embodiment of the present invention. Figure 2 is a partly sectional end view of the stator frame including the power crossover leads at the inlet end of the pump illustrated in Figure 1 and taken along line 2-2. Figure 3 is a longitudinal sectional view of the pump inlet end including the stator frame illustrated in Figure 2 taken along line 3-3. Figure 4 is an enlarged longitudinal sectional view of a portion of the stator frame illustrated in Figure 3 showing in more particularity an exemplary one of the power crossover leads having three joined together conductors surrounded by tubular electrical insulation bushings. Figure 5 is an exploded view of the three joined together conductors surrounded by tubular electrical insulation bushings of the crossover lead illustrated in Figure 4. Figure 6 is an enlarged sectional view of an exemplary joint between two of the crossover lead conductors illustrated in Figure 4. DESCRIPTION OF THE PREFERRED EMBODIMENT(S) Illustrated schematically in Figure 1 is an exemplary double stator, annular linear induction, or electromagnetic, pump (ALIP) 10 configured for use in a liquid metal nuclear reactor (not shown). The pump 10 includes a central structural annular or cylindrical core 12 disposed coaxially about an axial, or longitudinal centerline axis 14. An annular, radially inner electrical stator 16 surrounds the core 12 and is disposed coaxially therewith, and an annular, radially outer electrical stator 18 is spaced radially outwardly from the inner stator 16 and is disposed coaxially therewith for defining an annular flow duct 20 therebetween. A cylindrical housing 22 surrounds the outer stator 18 and extends longitudinally from an inlet end to an outlet end of the pump 10. More specifically, the pump 10 includes a stator baseplate or frame 24 at its inlet end in accordance with the present invention. The frame 24 as shown in Figures 1 and 2 includes an annular, radially outer rim or casing 26 disposed coaxially with the centerline axis 14, and an annular, radially inner hub 28 disposed coaxially and concentrically with the outer casing 26 about the centerline axis 14 which is spaced radially inwardly from the casing 26 to define an annular bellmouthed inlet channel 30 therebetween for receiving a liquid metal 32 such as liquid sodium for flow upwardly through the flow duct 20 and through a second annular frame 34 at the outlet end of the pump 10. A conventional annular junction casing or box 36 extends coaxially with the second frame 34, and is disposed radially inwardly of the flow duct 20 for allowing the liquid metal 32 to be discharged from the flow duct 20 and flow radially outwardly from the junction box 36 through an annular outlet 38 disposed at the top of the housing 22 above the inner and outer stators 16, 18. In conventional operation, electrical current is suitably provided to both the inner and outer stators 16, 18 for generating a magnetic flux to propel the liquid metal 32 upwardly or linearly through the flow duct 20 from the inlet channel 30 in the frame 24 and out the outlet 38 in a conventionally known manner. In accordance with the present invention, electrical power is provided to the outer stator 18 through the junction box 36 without requiring conventional conduits or bellows extending axially upwardly from the outer stator 18, through the frame 34, and through the outlet 38 which would be subject to flow of the liquid metal 32 thereover. Electrical power is conventionally provided to the inner stator 16 also through the junction box 36, which is not the subject of the present invention. More specifically, in this exemplary embodiment of the pump 10, each of the inner and outer stators 16, 18 includes conventional electrical coils configured for receiving three-phase electrical power in a conventional manner. Accordingly, each of the stators 16, 18 includes three input leads and three respective output leads for carrying the three-phase current therethrough. The inner stator 16 is conventionally provided with three-phase power through the junction box 36 and is, therefore, not further described. However, the outer stator 18 utilizes the frame 24 at the inlet end, for example, of the pump 10 for carrying power thereto from the junction box 36 without requiring passage through the outlet 38. As illustrated in Figures 1 and 2, the frame 24 includes a plurality of circumferentially spaced apart spokes or struts 40 extending radially between the casing 26 and the hub 28 and through the inlet channel 30. The struts 40 are fixedly joined to the casing 26 and the hub 28 and may be formed integrally therewith such as in a common casting. At least one electrically insulated power crossover cable or lead 42 extends through the hub 28, through one of the struts 40, which may alternatively be referred to as a crossover strut 40, and through the casing 26 for carrying electrical current therethrough. Electrical power is initially carried in a conventional input lead 44 as shown in Figure 1 downwardly through the junction box 36 and between the core 12 and the inner stator 16, for example, to the frame 24. For the three-phase outer stator 18, three of the input leads 44 are provided. And, three corresponding output leads 46 extend from the frame 24 upwardly between the core 12 and the inner stator 16, for example, through the junction box 36, and upwardly to a conventional power supply (not shown). As shown in Figure 2, the frame 24 includes at least six struts 40, with eight struts 40 being shown, for use as respective crossover struts for respectively carrying six crossover leads 42 therein. The six crossover leads 42 are electrically joined to respective ones of the three input and three output leads 44, 46 for carrying electrical current to and from the outer stator 18 through the frame 24 in accordance with the present invention. Figure 3 illustrates in more particularity an exemplary one of the crossover leads 42, with all the crossover leads 42 being identical in this exemplary embodiment. On the left side of Figure 3, the crossover lead 42 carries current from one of the three input leads 44 axially downwardly into the hub 28; then radially through a respective strut 40 to the casing 26; and then axially upwardly into the space between the housing 22 and the outer stator 18 wherein it is conventionally electrically joined to the outer stator 18. On the right side of Figure 3, another crossover lead 42 is identically configured for providing a return current path from the outer stator 18 and through the frame 24 to a respective output lead 46. In this way, the crossover leads 42 extend through respective frame struts 40 and are, therefore, protected thereby from the liquid metal 32 channeled through the flow duct 20. Each of the crossover leads 42 is a discrete conductor which is disposed through a respective crossover passage 48 extending through the hub 28, the crossover strut 40, and the casing 26. Since the frame 24 in an exemplary embodiment is an electrically conducting metal member, and the crossover leads 42 are electrical conductors, each of the crossover passages 48 includes a tubular electrical insulator 50 therein for receiving the crossover lead 42 and electrically insulating the crossover lead 42 from the hub 28, the crossover strut 40, and the casing 26. An exemplary one of the crossover leads 42 is shown in more particularity in Figure 4 as a U-shaped assembly of three conductors in a complementary U-shaped crossover passage 48 having three portions. Each crossover passage 48 includes a straight first, or center, channel 48a extending radially from the hub 28 and through the crossover strut 40 into the casing 26, and may be integrally formed during the casting process of the frame 24, or may be conventionally drilled completely radially through the frame 24. The crossover passage 48 also includes a second, or hub, channel 48b extending axially upwardly and perpendicularly from the radially inner end of the center channel 48a to an axially inside surface of the hub 28 adjacent the inner stator 16. And, the crossover passage 48 includes a third, or casing, channel 48c extending axially upwardly and perpendicularly from the radially outer end of the center channel 48a to the axially inside surface of the casing 26 adjacent the outer stator 18 on the same axial side of the frame 24 as that of the hub channel 48b. In this way, the crossover passage 48 has a generally U-shape for carrying the crossover lead 42 from inside the inner stator 16 and radially through the frame 24 to outside the outer stator 18. Correspondingly, the crossover lead 42 is a three-piece member including a straight first, or center, conductor 42a extending through a portion of the center channel 48a; a second, or hub, conductor 42b extending axially through the hub channel 48b and fixedly and electrically joined to the inner end of the center conductor 42a; and a third, or casing, conductor 42c extending through the casing channel 48c and fixedly and electrically joined to the outer end of the center conductor 42a. Also in the preferred embodiment of the present invention, the electrical insulator 50 is a three-part member including a first, or center, bushing 50a surrounding the center conductor 42a in the center channel 48a and extending radially between the hub conductor 42b and the casing conductor 42c. The insulator 50 also includes a second, or hub, bushing 50b surrounding the hub conductor 42b in the hub channel 48b. And, the insulator 50 also includes a third, or casing, bushing 50c surrounding the casing conductor 42c in the casing channel 48c. The crossover leads 42 are preferably copper, and the electrical insulator 50 is preferably in the form of conventional ceramic bushings for electrically insulating the crossover lead 42 from the frame 24 itself. The insulator bushings 50a, 50b, 50c provide a suitably close fit, subject to conventional manufacturing tolerances, surrounding the respective conductors 42a, 42b, 42c and within the respective channels 48a, 48b, 48c. Since the bushings 50b and 50c are disposed perpendicularly to the center bushing 50a in the U-shaped configuration, the radially outer and inner ends of the center conductor 42a are not directly insulated in this exemplary configuration. Accordingly, a conventional ceramic potting compound or cement 52 is disposed in both radially outer and inner ends of the center channel 48a and abuts the respective ends of the bushings 50a, 50b, and 50c for fully electrically insulating the crossover lead 42 from the frame 24. As shown in Figure 4, the center channel 48a preferably extends completely radially through the frame 24 from the casing 26 to the hub 28 and includes an inlet or access port 54 in the perimeter of the casing 26 sized for receiving both the center conductor 42a and the center bushing 50a during the assembly process. More specifically, Figure 5 illustrates an exploded view of the crossover lead 42 and the electrical insulator 50 for assembly into the frame 24. In this exemplary configuration, the center conductor 42a and the center bushing 50a are inserted into the center channel 48a through the access port 54 in any suitable order, or together if desired, for suitably positioning these parts within the center channel 48a. The hub and casing conductors 42b and 42c are then inserted downwardly through the respective hub and casing channels 48b and 48c into position in abutting contact with the center conductor 48a. Conventional brazing material 56 in the exemplary initial form of washers are positioned between the inner ends of the conductors 42b, 42c and the center conductor 42a. The hub and casing bushings 50b and 50c are then inserted over the conductors 42b and 42c into the respective hub and casing channels 48b and 48c to center and support the conductors 42b, 42c. This process is repeated for all of the desired crossover leads 42 and then the entire frame 24 is placed in a conventional furnace for heating the crossover leads 42 and the brazing material 56 to melt the brazing material 56 for effecting furnace brazing of the ends of the hub and casing conductors 42b and 42c to the center conductor 42a. Upon cooling of the frame 24, the hub and casing conductors 42b and 42c are, therefore, fixedly and electrically joined to the center conductor 42a by the brazing material 56. As shown in Figures 5 and 6, the hub conductor 42b and the casing conductor 42c have distal ends in the exemplary form of tenons, and the center conductor 42a includes a pair of mortises 58 for receiving respective ones of the hub and casing conductor tenons. The brazing material washers 56 may be initially sized to fit over the tenons and inside the mortises 58 prior to being melted. Upon melting of the brazing material 56, the brazing material 56 completely fills the joint between the conductor tenons and the mortises 58 by capillary action for providing a strong mechanical and electrical joint for carrying electrical current through the conductors 42a, 42b, and 42c. As shown in Figure 4, the potting cement 52 may be inserted into the center channel 48a from either end if accessible, or the hub and casing bushings 48b and 42c may be temporarily removed for allowing the potting cement 52 to be injected into the hub and casing channels 48b and 48c prior to reinstallation of the bushings 50b and 50c which are also, thereby, cemented into the respective channels 48b and 48c. A suitable metal plug 60 may then be conventionally welded in the access port 54 to complete the final assembly of the frame 24. The radially inner end of the center channel 48a may either be a blind hole requiring no further enclosing structure; or may similarly use another one of the plugs 60 where space permits assembly thereof; or in the embodiment illustrated in Figure 4, the core 12 itself provides closing of the inner end of the center channel 48a. Accordingly, the power leads 44 and 46 for the outer stator 18 may be routed from the junction box 36 above the inner stator 16, axially downwardly along the inner stator 16, radially through the crossover struts 40, and upwardly into the outer stator 18. In this way, conventional conduits and bellows for carrying power leads through the pump outlet 38 are not required, and the flow-induced vibration thereof and possibility of sodium leaking therein are eliminated. Of course, the crossover leads 42 could, alternatively, be suitably configured in the second frame 34 if desired, or at any other suitable position between the pump inlet channel 30 and its outlet 38 as desired. Various changes may be made to the above described embodiment. For example, although the invention has been described with respect to a three-phase outer stator 18 joined in series with the inner stator 16 and having six-crossover leads 42, the outer stator 18 can have any other type of electrical configuration including being joined in parallel with the inner stator 16 in a conventional delta configuration requiring only three crossover leads 42.

Claims: A stator frame 24 for an electromagnetic pump 10 comprising: an annular, radially outer casing 26; an annular, radially inner hub 28 disposed coaxially with said casing 26 and spaced radially inwardly therefrom to define an annular inlet channel 30 therebetween; a plurality of circumferentially spaced apart struts 40 extending radially between said casing 26 and said hub 28 and through said inlet channel 30; and at least one power crossover lead 42 extending through said hub 28, through a crossover one of said struts 40, and through said casing 26 for carrying electrical current therethrough, a crossover passage 48 extending through said hub 28, said crossover strut 40, and said casing 26 for receiving said crossover lead 42 therein; and said crossover passage 48 having a tubular electrical insulator 50 therein for receiving said crossover lead 42 for electrically insulating said crossover lead 42 from said hub 28, said crossover strut 40, and said casing 26, characterised in that said crossover passage 48 includes a center channel 48a extending radially from said hub 28 and through said crossover strut 40 into said casing 26; a hub channel 48b extending perpendicularly from an inner end of said center channel 48a to an inside surface of said hub 28; and a casing channel 48c extending perpendicularly from an outer end of said center channel 48a to an inside surface of said casing 26; said crossover lead 42 includes a center conductor 42a extending through said center channel 48a; a hub conductor 42b extending through said hub channel 48b and electrically joined to said center conductor 42a; and a casing conductor 42c extending through said casing channel 48c and electrically joined to said center conductor 42a; and said electrical insulator 50 includes a center bushing 50a surrounding said center conductor 42a in said center channel 48a and extending radially between said hub conductor 42b and said casing conductor 42c; a hub bushing 50b surrounding said hub conductor 42b in said hub channel 48b; and a casing bushing 50c surrounding said casing conductor 42c in said casing channel 48c. A stator frame according to claim 1 wherein said center channel 48a includes an access port 54 in the perimeter of said casing 26 sized for receiving both said center conductor 42a and said center bushing 50a. A stator frame according to claim 1 wherein said casing conductor 42c and said hub conductor 42b are fixedly and electrically joined to said center conductor 42a by brazing material 56. A stator frame according to claim 3 wherein said casing conductor 42c and said hub conductor 42b have distal ends in the form of tenons, and said center conductor 42a includes a pair of mortises 58 for receiving respective ones of said hub and casing conductor tenons. A stator frame according to claim 1 wherein said electromagnetic pump 10 includes a three-phase electrical stator 18 having three input leads 44 and three output leads 46, and said frame 24 includes six of said crossover struts 40 and six of said crossover leads 42 therein, respectively, and each of said crossover leads 42 is electrically joinable to a respective one of said three input and output leads 44, 46 for carrying electrical current to and from said electrical stator 18. A stator frame in accordance with claim 5 in combination with a double stator electromagnetic pump 10 wherein said electrical stator 18 is a radially outer stator 18 disposed radially outwardly of a radially inner stator 16 and having an annular flow duct 20 disposed radially therebetween and in flow communication with said frame inlet channel 30.

Inventors: FANNING ALAN WAYNE, OLICH EUGENE ELLSWORTH, FANNING, ALAN WAYNE, OLICH, EUGENE ELLSWORTH
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1994
Main classification: H02K44
IPC codes: H02K44, H02K5, G21C15